Also install the Adafruit Unified Sensor library in the same way:
We also have a great tutorial on Arduino library installation at:
http://learn.adafruit.com/adafruit-all-about-arduino-libraries-install-use (https://adafru.it/aYM)
Load Demo
Open up File->Examples->Adafruit_Si7021->si7021 and upload to your Arduino wired up to the sensor
Thats it! Now open up the serial terminal window at 115200 speed to begin the test.